1. Field of the Art
This invention relates to an apparatus and a method for drying wet substrates, for example, of liquid crystal panels and the like by the use of air knife effects.
2. Prior Art
For instance, a TFT type LCD panel is basically constituted by a couple of rectangular glass substrate plates with a TFT layer and a color filter layer, respectively. In the fabrication of TFT substrates, a process which consists of formation of a resist film, exposure, development, etching, defoliation of the resist film etc. is cyclically repeated for a plural number of times. the substrates need to be washed and dried repeatedly before or after these processes. On the other hand, a color filter is formed on substrates by photolithography, which also requires to wash and dry the substrate in preparatory and interim stages of its process. Further, washing and drying operations are similarly required in the case of LCD panels other than the TFT type panels or in the case of other substrates in the form of rectangular glass or synthetic resin plates.
For drying washed substrates, there have been known various methods. Particularly, in order to successively wash and dry substrates which are transferred on a processing line, it is the general practice to use the so-called air knife effects for drying purposes. Drying by air knife is usually used in the manner as follows.
By a substrate transfer means, the substrates to be dried are transferred in a horizontal state or in a slightly tilted state toward a direction perpendicular to the direction in which the substrates are transferred. An air knife nozzle with a narrow slit-like mouth is located in a position along a transfer path of substrates in such a way that the nozzle mouth is directed toward the top side of the substrates. As each substrate on the substrate transfer means is brought to a position where it is confronted by the air knife nozzle, air jets of high pressure are blasted across the entire length of the substrate in a direction perpendicular to the direction of transfer. Upon impinging upon the substrate, high pressure air is caused to flow along the surface of the substrate, peeling or scraping liquid droplets or films off the substrate surface for drying same.
In this connection, it is usually the case that the air knife nozzle is arranged in such a way as to spurt jet air toward a substrate in a direction opposite to the substrate transfer direction by the substrate transfer means and with a shallow angle of incidence on the drying surface of the substrate, and the slit-like mouth of the air knife nozzle is located in the proximity of the drying surface of the substrate. Accordingly, an extremely thin foil of jet air is blasted on the drying surface of the substrate with a predetermined angle of incidence, urging a liquid on the drying surface to move in rearward directions by the jet air pressure and finally purging the liquid from rear edge portions of the substrate.
In the case of substrates which are rectangular in shape, for example, each substrate is placed on the substrate transfer means in such a way that the opposite longitudinal sides of the substrate lie in the substrate transfer direction. In order to remove a liquid smoothly in a reliable manner from the surface of a substrate which is being transferred in the way as just mentioned, it is desirable to locate an air knife nozzle in a plane parallel with the substrate on the transfer means and with a certain angle of inclination relative to a direction which is perpendicular to the substrate transfer direction. Most preferably, the air knife is set in a position which is inclined through 45 degrees. By so setting, a liquid which is subjected to jet air pressure is urged to move along the surface of a substrate not only in the substrate transfer direction but also in obliquely sideward directions depending upon the angle of inclination of the air knife nozzle. As a consequence, a liquid on the substrate can be purged from its rear end edges in the direction of the substrate transfer direction and from its side edges as well, making it possible to remove a liquid in a smooth and quick manner by shortening the distances of movement of the liquid to the purging edges.
The inclined installation of an air knife nozzle, however, causes a liquid on a substrate to concentrate toward corner portions of purging rear edges of the substrate. In this regard, since the pressure of jet air from the air knife nozzle acts uniformly across a substrate, it is often found difficult to remove completely a liquid which has concentrated in corner portions of the substrate, especially in case the deposition rate of liquid on substrate surfaces is large. If, due to incomplete dissipation, substrates which still bear liquid residues in corner portion are transferred to a next stage of a fabrication process, the residual liquid may be forced to flow back onto the substrate surfaces by vibrations in the course of the transfer and may contaminate the substrates, leaving stains on the substrate surfaces. Besides, liquid residues in corner portions of substrates may deposit on the transfer means. The path of transfer by the substrate transfer means should be kept perfectly in a dry state because deposition of liquid on the transfer means may give rise to stains or other contaminations on the surfaces of following substrates.
On the other hand, for drying substrates, an air knife which is used in the drying stage is located within a drying chamber for the purpose of preventing redeposition of droplets or mist of dissipated liquids. In addition, it is necessary to make sure that two of the substrate will not simultaneously come into a blasting area of the air knife nozzle. If the above-mentioned inclination angle of the air knife nozzle is increased for the purpose of accelerating liquid dissipation, it will become necessary to broaden the intervals of the substrates on the transfer means and to provide a larger chamber in the drying stage.
In view of the foregoing situations, although the inclination angle of an air knife is preferred to be set at 45 degrees from the standpoint of drying efficiency, actually there often arises a necessity for reducing the inclination angle of the air knife nozzle, more specifically, for installing the air knife nozzle almost at right angles in order to reduce the drying chamber in size and to shorten the intervals between the individual substrates in transfer. In such cases, a liquid tends to move along lateral side edges of substrates in the transfer direction and to concentrate in corner portions of the substrates instead of bcing dissipated therefrom, making its removal more difficult.
In view of the difficulties as discussed above, it is an object of the present invention to provide a method and an apparatus for drying substrate plates efficiently and completely including corner portions of the substrates in a drying stage which is equipped with an air knife nozzle.
It is another object of the present invention to provide a method and an apparatus which permit to downsize a chamber of a drying stage and to narrow the intervals between individual substrate plates being conveyed by a transfer means, and yet make it possible to dry the surfaces of the respective substrates completely.
It is still another object of the present invention to a method and an apparatus which can purge a liquid in a reliable manner from corner portions of substrate plates where a liquid tends to concentrate when swept by jet air from an air knife nozzle which is disposed at a smaller angle of inclination.
According to the present invention, for achieving the above-stated objectives, there is provided an apparatus for drying substrate plates, which comprises: a substrate transfer means adapted to transfer washed thin substrate plates forward in a horizontal posture or in a predetermined tilted posture; an air knife nozzle located in a predetermined position by a path of transfer of the substrate transfer means to blast away and dry off a wash liquid remaining on surfaces of each substrate plate on the substrate transfer means; the air knife nozzle having a slit-like nozzle mouth located substantially at a uniform distance across a width of a drying surface of the substrate and disposed at a predetermined angle with a transverse direction perpendicular to the substrate transfer direction to spurt jet air across entire width of the substrate in a direction opposite to the substrate transfer direction and with a predetermined angle of incidence; and jet air augmenting means for increasing an amount of jet air to be blasted on and around a corner portion of the substrate which is finally swept by the air knife nozzle and to which a wash liquid on the drying surface is gathered by jet air from the air knife nozzle.
As for the air augmenting means, it may be constituted by an auxiliary jet air nozzle located face to face with the corner portion of the substrate which is finally swept by the air knife nozzle, and adapted to spurt liquid purge air toward the corner portion in the wake of the air knife nozzle. In this regard the auxiliary jet air nozzle may be adapted to start spurting liquid purge air toward the corner portion of the substrate at a time point when the corner portion comes to a confronting position, or adapted to spurt liquid purge air continuously toward the corner portion of the substrate. From the standpoint of accuracy of drying operation, it is preferable to control the auxiliary jet air nozzle to start spurting jet air at a time point when a corner portion of a substrate is advanced to a face-to-face confronting position. Further, the auxiliary jet air nozzle which serves to spurt jet air exclusively to one corner portion of each substrate suffices to be short in length, so that, even if located at a large angle relative to a direction perpendicular to a substrate transfer direction, it will affect the size of drying chamber and the intervals of substrate plates on the substrate transfer means. Accordingly, as compared with the air knife nozzle, it is preferable to set the auxiliary jet air nozzle at a greater inclination angle relative to a direction perpendicular to the substrate transfer direction. Liquid can be purged from a corner portion of a substrate in a more assured manner in case the incident angle of jet air from the auxiliary jet air nozzle is greater than that of jet air from the air knife nozzle.
For example, the above-mentioned substrates are thin synthetic resin or metal plates of square or rectangular shape. In case of rectangular plates, the substrates are placed on the substrate transfer means with the respective longitudinal sides of the plates in the transfer direction. In this connection, a roller conveyer or a belt conveyer can be suitably employed as the substrate transfer means. The substrates may be transferred either in a horizontal state or in a tilted state having one longitudinal or lateral side inclined upward or downward. In the case of the transfer in a tilted state, a liquid on the surface of a substrate is urged to flow along the sloped surface and therefore droplets of a liquid can be removed before sweeping the substrate surface with jet air from the air knife nozzle, enhancing the drying efficiency all the more.
As for another example of the air augmenting means, the air knife nozzle itself can be made to function as an air augmenting means. More particularly, the transfer speed by the substrate transfer means may be slowed down or the substrate transfer means may be stopped temporarily when the air knife nozzle comes face to face with a rear end corner portion of a substrate, which is finally swept by jet air from the air knife nozzle. By slowing down or stopping the substrate transfer means, an increased amount of air is blasted in the final corner portion of the substrate. For this purpose, the air augmenting means may be constituted by a substrate position detection means adapted to detect position of a substrate advancing on the substrate transfer means, and a control means, and a control means adapted to slow down the transfer speed or to temporarily stop the substrate transfer means when the substrate is detected by the substrate position detection means to have come to a point immediately upstream of a face-to-face position with the air knife nozzle.
Further, according to the present invention, there is provided a method for drying washed substrates by blasting jet air successively on surfaces of the substrates from an angular direction while being transferred by a substrate transfer means, characterized in that the method comprises the steps of: sweeping a drying surface of a substrate on the substrate transfer means with jet air from an air knife nozzle located substantially at uniform distance across a width of the substrate and adapted to bombard the jet air from an angular direction and with a predetermined angle of incidence in a substrate transfer direction thereby to scrape and dry off a liquid from surfaces of the substrate; and augmenting an amount of jet air when coming to a comer portion of the substrate from which a liquid is finally purged.
According to a modified form of the present invention, there is provided a method for drying washed substrates by blasting jet air successively on surfaces of the substrates from an angular direction while being transferred by a substrate transfer means, characterized in that the method comprises the steps of: sweeping a drying surface of a substrate on the substrate transfer means with jet air from an air knife nozzle located substantially at a uniform distance across a width of the substrate and adapted to bombard the jet air from an angular direction and with a predetermined angle of incidence in a substrate transfer direction thereby to scrape and dry off a liquid from surfaces of the substrate; and blasting a predetermined amount of liquid purge air to a comer portion of the substrate from an auxiliary jet air nozzle tufter the corner portion has been swept by jet air from the air knife nozzle.
The above and other objects, features and advantages of the present invention will become apparent from the following particular description of the invention, taken in conjunction with the accompanying drawings which show by way of example some preferred embodiments of the invention.